This invention relates to low odor surfactants and process for preparing same.
In the art of cleaning compositions for use in cleaning hard surfaces, particularly the art of cleaning tableware and other food-soiled utensils in machine dishwashers, the problem of excess foam buildup in the machine during operation as the result of high food soil concentrations was present. Also the machine dishwashing compositions had the tendency to foam excessively and/or leave undesirable spots and streaks on dishes and glassware. The conventional low foaming nonionic surfactants contained in such detergent compositions were ineffective in most cases in both removing food soil and providing suitable foam control where the aqueous cleaning solution became contaminated with foam generating protein soils such as egg soil and soil from various milk products.
The generation of such foams is particularly insidious in that the cleaning action of the machine dishwasher depends to a large extent upon the effective suppression of foam generation during operation. Without effective foam suppression, the mechanical cleaning action of the machine dishwasher is reduced as the result of foam buildup in the aqueous cleaning solution so that the aqueous washing fluid which is normally impelled against the tableware in the machine dishwasher is less effective in cleaning because it is forced against the tableware at reduced pressure. These problems have been largely solved by the use of alkyl phosphate ester defoamers such as monostearyl acid phosphate as disclosed in U.S. Pat. No. 3,314,891. While the use of monostearyl acid phosphate is effective for defoaming dishwasher compositions incorporating it, it presents problems when relatively low temperature water is employed, i.e., about 100.degree. F. or less.
A series of nonionic surfactants, certain members of which possess a relatively low cloud point as measured in a 1 percent aqueous solution, are available. Such surfactants are suggested for use in the formulation of machine dishwashing detergents and generally for use where a defoamer is necessary and where it is desired to employ a washwater temperature of about 100.degree. F. or less. These compounds are prepared using an active hydrogen terminated initiator which is prepared in much the same way as the polymers of U.S. Pat. No. 3,036,118 by first oxyethylating the initiator compound and subsequently oxypropylating the resulting compound to produce the nonionic surface active agent as more completely described in U.S. Pat. No. 3,036,118 incorporated herein by reference. U.S. Pat. Nos. 4,244,832; 4,272,394; and 4,306,987 provide a disclosure of dishwashing detergents containing such nonionic surfactants. The latter two patents disclose the use of low foaming nonionic surfactants of five different generalized formulas, all of which are terminated by chains of oxypropylene groups or groups with greater than three carbon atoms. While such dishwashing detergent compositions may be used at washwater temperatures below 100.degree. F. and even as low as 80.degree. F. and are low foaming, they present a problem not presented by the preferred composition of U.S. Pat. No. 3,314,891. The preferred compositions of this latter patent rather than being terminated with oxypropylene groups or oxyalkylene groups having more than three carbon atoms, are terminated with oxyethylene rich groups. The oxypropylene group terminated compounds have the disadvantage in that the commercially produced products generally have what might be considered a typical polyoxypropylene odor due to the presence of various impurities such as allyl alcohol, substituted dioxolanes and allyloxypropan-2-ol which are byproducts of the oxypropylation reactions. The preferred compounds of U.S. Pat. No. 3,314,891 do not present this problem because the polyoxyalkylene surfactants employed in the preferred composition are oxyethylene terminated compounds.
Many impurities that are formed in preparing such oxyalkylene compounds are further reacted with ethylene oxide and thus are eliminated or substantially reduced in the oxyethylene terminated compounds. However, the oxypropylene terminated compounds, on the other hand, do not do this and as a result there is a buildup of these impurities. Accordingly, it is a purpose of the instant invention to eliminate or substantially reduce odor problems in low foaming dishwashing detergent compositions which employ polyoxyalkylene polyols which are terminated with oxypropylene groups. Similar odor problems may also be presented by rinse aid compositions used in dishwashing detergents which employ such oxypropylene group terminated polyoxyalkylene polyethers.